Microsoft has confirmed that some users are experiencing a problem with emails being marked as spam and blocked when they try to send them to Gmail accounts, Bleeping Computer reports.

Outlook users are receiving a message from Gmail servers stating that their messages were suspicious and did not reach the recipient’s inbox. This issue only affects users with local domains, according to the support document.

“Remote server returned message detected as spam [..]. Gmail has detected that this message is likely suspicious due to the very low reputation of the sending domain. To best protect our users from spam, the message has been blocked,” this response is provided by the Gmail mail server.

Google’s support site says that most likely only a portion of these messages are blocked because they have a “high probability of being spam.”

Until the team resolves this new issue, Microsoft advises users to add an alias to their accounts and send emails to Gmail contacts using that alias.

Outlook aliases are additional email addresses associated with your account that use the same mailboxes, contact list, and account settings as your primary email address.

Users can log in to their accounts under any alias, as they all use the same credentials.

Although Microsoft has not shared the root cause of why emails are being flagged as spam and blocked, Google suggests that the company reconsider its rules for bulk senders.

Currently, Google blocks emails sent by bulk senders who do not meet stricter spam thresholds and do not authenticate their messages, as required by new rules designed to strengthen protection against spam and phishing attacks.